174 BOTANICAL GAZETTE [February 



drawings are of bud, leaf-scar, pith, and other twig characters upon which the 

 keys are based, so that with the use of a hand lens it should be possible to 

 determine readily the genera, and for the most part the species, for native and 

 introduced trees and shrubs. The author is to be congratulated in making 

 such a fund of unusual information available in such a compact and readily 

 available form. — Geo. D. Fuller. 



American trees. — Another book on trees, by Emerson and Weed,s has 

 been added to the already large number upon the same subject. It is essen- 

 tially a book for the amateur, since its chief virtue lies in the excellent photo- 

 graphs by Emerson, an entire page being devoted to each species. The absence 

 of keys of any sort renders the book comparatively useless for the identification 

 of an unknown species, but the quality and abundance of the illustrations 

 will make it one the tree lover will wish to have upon his table. — Geo. D. 

 Fuller. 



NOTES FOR STUDENTS 



Physiological balance in soil and other nutrient solutions. — Hibbard^ 

 has just published a piece of work on physiological balance in soil solution which 

 is to mark a decided advance (both theoretically and practically) , if the future 

 development of the work approximates its present promise. He extracted the 

 soil solution from an infertile very sandy soil and from a fertile sandy loam by 

 the Van Suchtelen oil pressure method as improved and extended in usefubess 

 by Morgan. 7 Hibbard speaks of this as giving a more concentrated solu- 

 tion than any other extraction method. The solution thus extracted from the 

 poor sandy soil had an osmotic pressure of o . 193 atmospheres, and that from the 

 good soil 1 .81 atmospheres. The soil extracts showed an order of production 

 similar to the soils from which they came. 



The soil extracts were used instead of distilled water to prepare the Shive 

 3-salt (KH2PO4, CaCNOj)^, MgS04) nutrient solution. The total concentra- 

 tion of nutrient salts added gave an osmotic pressure of 1.75 atmospheres, 

 and in the 36 different solutions made up from each soil extract and from dis- 

 tilled water the proportions of each salt varied from 10 to 80 per cent of the 

 total nutrient salt osmotic concentration. 



In the nutrient solution made from the extract of the poor soil the optimum 

 osmotic proportions of the KH.PO4, Ca(N03)2, and MgS04 for the growth of 

 Fultz wheat were 7:1:2 respectively, with a total osmotic pressure of (i . 75+ 

 o . 193) 1 . 94 atmospheres ; in that made from the extract of the good soil 2:7:1 

 respectively, with a total osmotic pressure of (i .75 + 1 -81) 3.56 atmospheres; 

 and in that made with distilled water 5:2:3, with a total osmotic pressure of 



s Emerson, Arthur I., and Weed, C. M., Our trees, how to know them. New 

 ed. pp. xxi-l-295. pis. 149. Philadelphia: Lippincott Co. $3-50- 



(• Hibbard, R. P., Physiological balance in the soil solution. Tech. Bull. Mich. 

 Agric. Exper. Sta. no. 40. pp. 44. 191 7. 



7 Tech. Bull. Mich. Agric. Coll. Exp. Sta. no. 28. 



